Engine control device

ABSTRACT

An engine control device includes an electronic control unit. The electronic control unit is configured to perform a spark discharge with an ignition plug for each cylinder by cutting off energization after elapse of a predetermined period from start of energization to an ignition coil for each cylinder of the engine, to stop the spark discharge caused by the ignition plug for each cylinder after supply of fuel to the engine is stopped when operation of the engine is stopped, and to control an ignition plug so as to stop the spark discharge caused by the ignition plug from a cylinder after a rotation speed of a crankshaft decreases gradually and the rotation speed of the crankshaft reaches a preset threshold value or less, after the stop of the supply of fuel to the engine.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2017-026602 filed onFeb. 16, 2017 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a control device that stops the supplyof fuel to an engine and ignition of the fuel to stop the operation ofthe engine, and particularly, to a spark discharge caused by an ignitionplug for each cylinder.

2. Description of Related Art

Generally, a system (stop and start system), which automatically stopsan engine of a vehicle during idling or the like and then automaticallyrestarts the engine, is well-known in the related art. When the engineis stopped in the system as described above, normally, a throttle valveis closed, supply of fuel by an injector is stopped (fuel cut), andthen, a spark discharge caused by an ignition plug is continued for awhile, and the spark discharge caused by the ignition plug is stoppedwhen unburned fuel remaining within a cylinder is combusted (refer toJapanese Unexamined Patent Application Publication No. 2010-255591 (JP2010-255591 A)).

SUMMARY

However, in a case where the spark discharge caused by the ignition plugis continued for a while after a fuel cut as described above, theduration time of the spark discharge caused by the ignition plug becomesa problem. That is, when the time for which the spark discharge causedby the ignition plug is continued is significantly shorter than usual,the unburned fuel within the cylinder cannot be sufficiently combustedand may be released into the ambient air. Thus, there is a possibilitythat aggravation of emissions is caused. On the other hand, continuingan unneeded spark discharge caused by the ignition plug until afterunburned fuel is substantially exhausted leads to an increase inwasteful power consumption.

Energization time may become extremely long due to the reverse operationof a crankshaft immediately before the stop of the engine. As a result,degradation of the ignition coil may be accelerated, and there is also apossibility that the service life of the ignition coil is shortened. Indetail, first, when a fuel cut occurs as described above, the crankshaftrotates with inertia for a while after that, and the kinetic energy of arotating part becomes gradually small with a decrease in the rotationspeed of the crankshaft.

Thus, the crankshaft is not able to exceed a top dead center in acompression stroke of one of the cylinders. As a result, the crankshaftis reversely operated before the top dead center after being stoppedfirst. In this case, normally, there is a case where the energizationcutoff timing of the ignition coil set in the vicinity of the top deadcenter may not be reached. Therefore, when the energization to theignition coil is started before the reverse operation of the crankshaft,the energization may continue even during the elapse of a guard time setfor the protection of the ignition coil.

The present disclosure provides an engine control device that, by virtueof a suitable spark discharge caused by the ignition plug after a fuelcut at an engine stop, further suppresses wasteful power consumptionwithout causing aggravation of emissions and further restrains prematuredegradation of an ignition coil.

A first aspect of the present disclosure relates to an engine controldevice including an electronic control unit. The electronic control unitis configured to perform a spark discharge with an ignition plug foreach cylinder by cutting off energization after elapse of apredetermined period from start of energization to an ignition coil foreach cylinder of the engine, and to stop the spark discharge caused bythe ignition plug for each cylinder after supply of fuel to the engineis stopped when operation of the engine is stopped.

Also, the electronic control unit is configured to control an ignitionplug so as to stop the spark discharge caused by the ignition plug froma cylinder after a rotation speed of a crankshaft decreases graduallyand the rotation speed of the crankshaft reaches a preset thresholdvalue or less, after the stop of the supply of fuel to the engine. Thecrank rotation speed may have, for example, a value obtained byaveraging rotation speeds calculated based on crank signals, and may bea so-called engine speed.

According to the first aspect of the present disclosure, first, when afuel cut is performed in order to stop the operation of the engine andthe rotation speed of the crankshaft that rotates with inertia decreasesgradually, and when the rotation speed of the crankshaft is higher thanthe preset threshold value, the spark discharge caused by the ignitionplug is continued and unburned fuel within the cylinder is combusted. Onthe other hand, when the crank rotation speed becomes the thresholdvalue or less, the spark discharge caused by the ignition plug isstopped, and wasteful power consumption is further suppressed. Since apossibility that the crankshaft is reversely operated after the start ofthe energization to the ignition coil becomes low, a situation in whichthe energization time becomes extremely long as described above can befurther suppressed.

In the engine control device according to the first aspect of thepresent disclosure, the threshold value may be set to such a rotationspeed that the crankshaft is reversely operated in accordance with acompression reaction force of the cylinder when the rotation speed ofthe crankshaft becomes lower than the threshold value. According to thefirst aspect of the present disclosure, the crankshaft is no longerreversely operated after the start of the energization to the ignitioncoil, and the energization time to the ignition coil can be furtherrestrained from becoming extremely long. Therefore, the wasteful powerconsumption can be further suppressed without causing aggravation ofemissions, and premature degradation of the ignition coil can be furtherrestrained.

Similar to a first aspect of the present disclosure, a second aspect ofthe present disclosure relates to an engine control device including anelectronic control unit. The electronic control unit is configured toperform a spark discharge with an ignition plug for each cylinder bycutting off energization after elapse of a predetermined period fromstart of energization to an ignition coil for each cylinder of theengine, to stop the spark discharge caused by the ignition plug for eachcylinder of the engine after supply of fuel to the engine is stoppedwhen operation of the engine is stopped, and to retard an energizationstart timing to an ignition coil as a rotation speed of a crankshaftbecomes lower when the rotation speed of the crankshaft decreasesgradually after the stop of the supply of fuel to the engine.

According to the second aspect of the present disclosure, the unburnedfuel within the cylinder is combusted by the spark discharge caused bythe ignition plug being continued even after a fuel cut is performed inorder to stop the operation of the engine, first. In this case, sincethe energization start timing to the ignition coil is retarded by theelectronic control unit as the rotation speed of the crankshaft thatrotates with inertia decreases gradually, the energization time to theignition plug becomes short, and the wasteful power consumption isfurther suppressed.

Since the energization start timing to the ignition coil is retarded asdescribed above, the energization time becomes shorter as the start ofthe energization becomes slower, even when the crankshaft is reverselyoperated and thereafter the energization cutoff timing is not reached asdescribed above. That is, a situation in which the energization time tothe ignition coil becomes extremely long due to the reverse operation ofthe crankshaft can be further suppressed, and the premature degradationof the ignition coil can be further restrained.

In the engine control device according to the second aspect of thepresent disclosure, the electronic control unit may be configured toretard an energization start timing to the ignition coil until after acompression top dead center of a cylinder when the rotation speed of thecrankshaft becomes equal to or lower than a preset threshold value.According to the second aspect of the present disclosure, when thecrankshaft is reversely operated before the compression top dead centerof the cylinder, the energization to the ignition plug is not started.Thus, there is no case where the energization time to the ignition coilbecomes extremely long as described above due to the reverse operationof the crankshaft.

Similar to the first and second aspects of the present disclosure, athird aspect of the present disclosure relates to an engine controldevice including an electronic control unit. The electronic control unitis configured to perform a spark discharge with an ignition plug foreach cylinder by cutting off energization after elapse of apredetermined period from start of energization to an ignition coil foreach cylinder of the engine, and to stop the spark discharge caused bythe ignition plug for each cylinder of the engine after supply of fuelto the engine is stopped when operation of the engine is stopped. Theengine control device cuts off the energization to the ignition coileven before the elapse of the predetermined period in a case where acrankshaft is reversely operated after the start of energization to theignition coil.

According to the third aspect of the present disclosure, the unburnedfuel within the cylinder is combusted by the spark discharge caused bythe ignition plug being continued even after a fuel cut is performed inorder to stop the operation of the engine, first. When the crankshaft isreversely operated after the rotation speed of the crankshaft thatrotates with inertia decreases gradually and the energization to theignition coil of one of the cylinders is started, the energization iscut off even before a predetermined period elapses since the start ofthe energization (that is, the energization cutoff timing is notreached).

That is, even when the crankshaft is reversely operated after the startof the energization to the ignition coil resulting from the sparkdischarge caused by the ignition plug as described above and theenergization cutoff timing is not reached, there is no case where theenergization time becomes extremely long as described above. Therefore,the wasteful power consumption can be further suppressed, and thepremature degradation of the ignition coil can be further restrained.

According to the control device of the aspect of the present disclosureas described above, when the operation of the engine is stopped, thespark discharge caused by the ignition plug is continued for a whileeven after the supply of the fuel is stopped. Accordingly, the unburnedfuel within the cylinder can be combusted. In the first aspect of thepresent disclosure, when the rotation speed of the crankshaft decreasesgradually and becomes equal to or lower than the threshold value, thespark discharge caused by the ignition plug is stopped. Accordingly, thewasteful power consumption can be further suppressed, and a situation inwhich the energization time to the ignition coil becomes extremely longcan be further suppressed.

In the second aspect of the present disclosure, the energization starttiming to the ignition coil is retarded as the rotation speed of thecrankshaft decreases gradually as described above. Accordingly, thewasteful power consumption can be further suppressed, and a situation inwhich the energization time to the ignition coil becomes extremely longcan also be further suppressed. In the third aspect of the presentdisclosure, the energization is cut off when the crankshaft is reverselyoperated. Accordingly, the energization time can be further restrainedfrom becoming extremely long.

Therefore, by virtue of the first to third aspects of the presentdisclosure, the wasteful power consumption can be further suppressedwithout causing the aggravation of emissions when the engine is stopped,the premature degradation of the ignition coil resulting from theenergization time becoming extremely long can be further restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the present disclosure will be described belowwith reference to the accompanying drawings, in which like numeralsdenote like elements, and wherein:

FIG. 1 is a schematic configuration view of an engine control devicerelated to an embodiment;

FIG. 2 is a timing chart illustrating an example of the engine speedwhen an engine is stopped, the rotation speed of a crankshaft, and thechanges of crank counter;

FIG. 3 is a flowchart illustrating a routine of stop and start controlrelated to the embodiment;

FIG. 4 is a flowchart illustrating a routine of automatic stopprocessing related to the embodiment;

FIG. 5 is a timing chart illustrating a decrease in crank rotation speedat an engine automatic stop, and spark discharge caused by an ignitionplug after a fuel cut;

FIG. 6 is a view equivalent to FIG. 4 related to Modification Example 1in which energization start timing is retarded in accordance with thedecrease in the crank rotation speed;

FIG. 7 is a view equivalent to FIG. 5 related to Modification Example 1;

FIG. 8 is a view equivalent to FIG. 4 related to Modification Example 2in which energization is immediately cut off when the crankshaft isreversely operated; and

FIG. 9 is a view equivalent to FIG. 5 related to Modification Example 2.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be describedwith reference to the drawings. The present embodiment is an example,and a case where an aspect of the present disclosure is applied to agasoline engine mounted on a vehicle will be described.

Outline of Engine

Although a schematic configuration of the engine 1 is illustrated inFIG. 1, the engine 1 of the present embodiment is a four-cylindergasoline engine, a piston 12 is accommodated in each of four first tofourth cylinders 2 (solely one is illustrated in the drawings) so as todefine a combustion chamber 11. The piston 12 and a crankshaft 13 arecoupled together by a connecting rod 14, and a crank angle sensor 101for detecting the rotational angle (crank angle) of the crankshaft 13 isprovided.

In detail, a signal rotor 17 is attached to the crankshaft 13, and aplurality of gear teeth 17 a is provided on an outer peripheral surfaceof the signal rotor 17. Meanwhile, the crank angle sensor 101 includes,for example, two electromagnetic pickups and is adapted to output apulse signal from each electromagnetic pickup whenever the gear teeth 17a of the signal rotor 17 passes due to the rotation of the crankshaft13.

A signal output from one of the two electromagnetic pickups is a cranksignal, and a signal output from the other electromagnetic pickup has apredetermined phase difference from the crank signal. For this reason,whether or not the crankshaft 13 is rotating normally (rotatingreversely) can be determined depending on whether the signal from theother electromagnetic pickup is any of low and high signals when thesignal from the one electromagnetic pickup rises or falls.

Although not illustrated, a flywheel is attached to an end part of thecrankshaft 13 so as to rotate integrally, and a starter motor 18(schematically illustrated in FIG. 1) is disposed so that a pinion gearcan be rotated in engagement with a ring gear formed at an outerperiphery of the flywheel. The starter motor 18 operates upon thereception of the signal from an ECU 100 as will be described belowduring the normal starting of the engine 1.

A cylinder head 16 is placed at an upper part of a cylinder block 15, aninjector 19 is disposed in each cylinder 2, to face the combustionchamber 11. For example, the fuel injected from the injector 19 in anintake stroke of the cylinder 2 forms an air-fuel mixture while ridingon the flow of intake air within the cylinder 2 and being diffused. Inorder to ignite the air-fuel mixture formed as described above, anignition plug 20 is disposed in the cylinder head 16 for each cylinder2.

An ignition coil 21 is directly attached to the ignition plug 20, andthe ignition coil 21 and an ignitor 22 are provided integrally with theignition coil 21 although these are separately illustrated in thedrawing for convenience. The ignitor 22 receives an energization signalfrom the ECU 100 to energize the ignition coil 21 (primary coil), andthen, receives a cutoff signal to rapidly cut off the energization,thereby causing a high voltage to be supplied from the ignition coil 21(from a secondary coil) to the ignition plug 20.

An intake port 30 and an exhaust port 40 are formed in the cylinder head16 so as to communicate with the combustion chamber 11 within eachcylinder 2, and openings that face the interiors of the respectivecylinders 2 are opened and closed by an intake valve 31 and an exhaustvalve 41. A valve train in which the intake valve 31 and the exhaustvalve 41 are operated includes two camshafts 32, 42 for intake andexhaust, and is rotated with the crankshaft 13 via a timing chain and asprocket that are not illustrated.

A cam angle sensor 102 is provided in the vicinity of the intakecamshaft 32 so as to output a pulse signal (hereinafter, referred to asa cam signal) when one of the cylinders 2 is at a predetermined crankangle position (for example, the first cylinder 2 is at a top deadcenter). Since the intake camshaft 32 rotates at half of the speed ofthe crankshaft 13, the cam angle sensor 102 outputs a cam signal atleast once whenever the crankshaft 13 makes two rotations (the crankangle varies 720°).

An air flow meter 103, an intake air temperature sensor 104 (built inthe air flow meter 103), and an electronic-control-type throttle valve33 are disposed in an intake passage 3 that communicates with anupstream side (upstream side of the flow of intake air) of the intakeport 30. The throttle valve 33 is driven by a throttle motor 34 so as tothrottle the flow of intake air to adjust the intake air amount of theengine 1.

As described above, the intake air of which the flow rate has beenadjusted by the throttle valve 33 flows into each cylinder 2 from theintake port 30, and is mixed with the fuel injected from the injector 19as described above, to form an air-fuel mixture. Then, the air-fuelmixture is ignited and combusted by the ignition plug 20 in a rear halfof a compression stroke, and thereby, the generated gas flows out theexhaust port 40 in an exhaust stroke of the cylinder 2. A catalyst 43for controlling exhaust gas is disposed in an exhaust passage 4 thatcommunicates with a downstream side (a downstream side of the flow ofexhaust gas) of the exhaust port 40, and an air-fuel-ratio sensor 105 isdisposed upstream of the catalyst 43.

ECU

The engine 1 configured as described above is controlled by the ECU 100.The ECU 100 is a well-known electronic control unit, and includes acentral processing unit (CPU), a read-only memory (ROM), and a randomaccess memory (RAM), and a backup RAM, or the like. The CPU executesvarious kinds of calculation processing based on control programs andmaps that are stored in the ROM. The RAM temporarily stores calculationresults in the CPU and the data input from the respective sensors, andthe backup RAM stores, for example, the data to be saved at the stop ofthe engine 1.

In addition to the crank angle sensor 101, the cam angle sensor 102, theair flow meter 103, the intake air temperature sensor 104, theair-fuel-ratio sensor 105, and the like, an accelerator sensor 106 thatdetects the operation amount (throttle valve opening degree) of anaccelerator pedal, a brake switch (brake SW) 107 that detects theoperation of a brake pedal, a starter switch (starter SW) 108 foractuating the starter motor 18, and the like are connected to the ECU100.

The ECU 100 controls the operational state of the engine 1 by executingthe various control programs based on the signals input from the varioussensors and the switches 101 to 108. For example, the ECU 100 executesfuel injection control using the injector 19 (the control of injectionamount and fuel injection timing), spark discharge caused by the ignitor22 (the control of ignition timing by the ignition plug 20), the controlof the throttle valve 33 by the throttle motor 34 (namely, the controlof the intake air amount), and the like.

The fuel injection control and the spark discharge as described aboveare performed at a suitable timing for each cylinder 2, and a crankcounter having two rotations (720° at the crank angle) of the crankshaft13 as one cycle is produced. As an example is illustrated in FIG. 2, thecrank counter is produced, for example, with a top dead center (#1TDC)of a first cylinder 2 as a reference, is reset in accordance with theinput of a cam signal at time t1 as illustrated at a lower stage of FIG.2, and is counted up in accordance with the input of the crank signalafter a counted value reaches 0.

When the starter SW 108 is turned on, the ECU 100 actuates the startermotor 18, rotates (cranks) the crankshaft 13, and executes the controlof fuel injection and ignition at starting to start (normal starting)the engine 1. As described below, the ECU 100 also executes an stop andstart control in which the engine 1 is automatically stopped in apredetermined situation, such as when a vehicle is stopped, and theengine 1 is restarted without using the starter motor 18 in accordancewith a driver's subsequent predetermined operation.

Stop and Start Control

The flow of overall processing of a stop and start control routine isillustrated in FIG. 3. The routine is repeatedly executed at apredetermined timing in the ECU 100. First, whether or not apredetermined automatic stop condition is satisfied during the operationof the engine 1 is determined in Step ST101. When the determination isnegative (NO), a return is made, and when the determination is positive(YES), the process proceeds to Step ST102 in which automatic stopprocessing of the engine 1 is executed.

The automatic stop condition may be set to include, as an example, theengine 1 being in an operating state, being in an accelerator-off state(the throttle valve opening degree is equal to or less than apredetermined threshold value and almost zero), being in a brake-onstate (a brake stepping force is equal to or more than a predeterminedthreshold value), and the vehicle speed being equal to or lower than apredetermined threshold value, or the like (a case where the engine isconsidered to be immediately before a stop or a case where the engine isconsidered to be substantially stopped.

Although the automatic stop processing of Step ST102 will be describedbelow in detail, the automatic stop processing is one in which the fuelinjection from the injector 19 is stopped (fuel cut), and ignitioncaused by the ignition plug 20 is also stopped slightly later.Accordingly, since the combustion torque of an air-fuel mixture is nolonger generated, the rotation speed of the crankshaft 13 that rotateswith inertia decreases gradually as illustrated in the FIG. 2.

When the rotation speed of the crankshaft 13 decreases gradually asdescribed above, it is preferable that the opening degree of thethrottle valve 33 is controlled in accordance with the degree ofdecrease of a crank rotation speed Nc (a value obtained by averaging therotation speeds of the crankshaft 13, and illustrated by a one-dot chainline in FIG. 2). For example, it is preferable to stop the operation ofan auxiliary machine used as an external load of the engine 1, such asan alternator or a compressor of an air-conditioner.

The stop of rotation of the crankshaft 13 is determined as will bedescribed below in detail (Step ST103). When the determination isnegative (NO), the process proceeds to Step ST108 (to be describedbelow) in which whether or not a predetermined restarting condition issatisfied is determined. When the determination is also a negativedetermination (NO), the process returns to Step ST102, whereas when thedetermination is positive (YES), the process proceeds to Step ST109 inwhich ignition starting processing of the engine 1 is performed to endthe routine (END).

The ignition starting processing is processing in which the engine 1 isrestarted by using the inertia of rotation of the crankshaft 13 withoutusing the starter motor 18, and is performed when a driver changeshis/her mind (Change Of Mind: COM) in the middle of an automatic stop ofthe engine 1 and starts the engine 1 again. Since the driver, forexample, releases the brake pedal and steps on the accelerator pedal insuch a case, the restarting condition of the engine 1 is satisfied.

When a cylinder 2 (for example, a third cylinder 2 at times t1 to t2described above with reference to FIG. 2) in a compression stroketransits to an expansion stroke beyond a top dead center (#3TDC), fuelis injected by the injector 19, and thereby, ignited by the ignitionplug 20 while waiting for an air-fuel mixture to be formed. Accordingly,a rotative force can be applied to a crankshaft 13, and the engine 1 canbe started without using the starter motor 18.

On the other hand, when a positive determination (YES) that the rotationof the crankshaft 13 is stopped is made in Step ST103, that is, when astop process of the engine 1 is completed, the process proceeds to StepST104 in which predetermined data is stored in the backup RAM. Theprocess proceeds to Step ST105 in which whether or not the restartingcondition of the engine 1 is satisfied is determined. When thedetermination is negative (NO), the process proceeds to Step ST106 inwhich whether or not an end condition of the stop and start control issatisfied, such as an ignition switch of the vehicle being turned off,is determined.

When the end condition is satisfied and the determination is positive(YES), the routine is ended (END), whereas when the end condition is notsatisfied and the determination is negative (NO), the process returns toStep ST105 in which the satisfaction of the restarting condition isdetermined again. When the restarting condition satisfies and thedetermination is positive (YES) while the waiting is performed asdescribed above, the process proceeds to Step ST107 in which the normalrestarting processing of the engine 1 is executed.

The restarting condition of the engine 1 in Step ST105 and ST108 may beset to include, for example, the stepping force of the brake pedal beingreduced and becoming smaller than the predetermined threshold value,accelerator stepping operation being performed, a predeterminedoperation of a shift lever being performed, or the like.

Although detailed description regarding the normal restarting processingis omitted, for example, the starter motor 18 is operated to startcranking, the injection of fuel by the injector 19 is started, and theignition caused by the ignition plug 20 is also started. Accordingly,when combustion is started in one of the cylinders 2 (initial explosion)and an engine speed increases to a predetermined value, the routine isended (completion of the starting) (END).

Engine Stop Determination

The determination of rotation stop of the crankshaft 13 in Step ST103 ofthe flow is described in detail. When the engine 1 stops, first, theengine speed decreases gradually as illustrated in an upper stage of theFIG. 2, and the rotation speed of the crankshaft 13 also decreases as awhole as illustrated in a middle stage of FIG. 2. Since intervals inwhich crank signals are input become long, as illustrated in a lowerstage of FIG. 2, the inclination of a graph of the crank countergradually becomes gentle.

In a process in which the engine 1 stops as described above, therotation of the crankshaft 13 is reduced in speed by an in-cylinderpressure (compression reaction force) that rises in the compressionstroke for each cylinder 2, and the rotation speed of the crankshaft 13decreases gradually as the piston approaches the top dead center (TDC)as illustrated in the middle stage of FIG. 2. On the other hand, whenthe piston transits to an expansion stroke beyond the top dead center,the rotation of the crankshaft 13 is shortly accelerated this time bythe in-cylinder pressure. Thus, the rotation speed of the crankshaft 13increases.

That is, the rotation speed of the crankshaft 13 decreases gradually asa whole as illustrated by the one-dot chain line in FIG. 2 whilerepeating a decrease and an increase before and after top dead centers(#1TDC, #3TDC, #4TDC, . . . ) of the respective cylinders 2.Accordingly, the inertia force of the rotation becomes small, and in theillustrated example, and after a top dead center (#3TDC) of a thirdcylinder 2 is exceeded at time t2, it is not possible to exceed a topdead center (#4TDC: does not reach) against the in-cylinder pressure ofa fourth cylinder 2 at time t3.

For this reason, the crankshaft 13 stops through a period of swing-backin which the crankshaft 13 is reversely operated after being stopped fora moment prior to the top dead center, and then is slightly operatedagain in a normal rotational direction. In this case, after thecrankshaft 13 is reversely operated at time t3, the crank counterdecreases in accordance with the crank signal. When the rotationaldirection is normal again at time t4, the crank counter increases attime t5.

When an angle at which the crankshaft 13 is rotated while being stoppedthrough the swing-back period as described above becomes small, thecrank signal is no longer output from the crank angle sensor 101. Whenthe time for which no crank signal is input as at times t5 to t6 reachesa preset time Δt (time t6), the rotation of the crankshaft 13 isdetermined to have stopped (that is, the engine 1 is determined to havestopped).

Spark Discharge Caused by Ignition Plug at Engine Stop

Meanwhile, as the automatic stop processing (Step ST102 of FIG. 3) ofthe engine 1, in the present embodiment, emissions are reduced bycontinuing the spark discharge caused by an ignition plug for a whileafter fuel is cut first, and by igniting unburned fuel within thecylinder 2 by the ignition plug 20. In this case, generally, anenergization start timing to the ignition coil 21 is before the top deadcenter of the cylinder 2, and an energization cutoff timing (namely, theignition timing of the ignition plug 20) is after the top dead center.

However, when the time for which the spark discharge caused by theignition plug is continued after a fuel cut as described above isexcessively longer than usual, there is a possibility that unneededspark discharge caused by the ignition plug may be performed even afterthe unburned fuel is substantially exhausted, and wasteful powerconsumption may increase extremely. Moreover, when the crankshaft 13 isreversely operated during energization to the ignition coil 21,energization time may become extremely long. As a result, there is apossibility that the wasteful power consumption may increase extremely,the degradation of the ignition coil 21 may be accelerated, and there isalso a possibility that the service life of the ignition coil 21 isshortened.

That is, as described above with reference to FIG. 2, immediately beforethe stop of the engine 1, the crankshaft 13 is reversely operated due toa rise in the in-cylinder pressure of one of the cylinders 2 prior tothe top dead center of the cylinder 2, and consequently, does not reachthe energization cutoff timing after the top dead center. For thisreason, when the energization to the ignition coil 21 is started beforethe reverse operation of the crankshaft 13 starts, the energizationcontinues until a guard time (for example, tens of milliseconds) set forthe protection of the ignition coil 21 elapses, and the time of theenergization becomes extremely long.

Thus, in the present embodiment, at an automatic stop of the engine 1,the spark discharge (namely, energization control to the ignition coil21) caused by the ignition plug is stopped after the crank rotationspeed Nc decreases gradually after a fuel cut and reaches a presetthreshold value Nc1 or less. When the crank rotation speed Nc becomeslower than the threshold value Nc1, the threshold value Nc1 is set to arotation speed that is considered that the crankshaft 13 is reverselyoperated due to the in-cylinder pressure (compression reaction force) ofthe cylinder 2 as described above.

In the following, the automatic stop processing of the engine 1 will bespecifically described in accordance with a flowchart of FIG. 4 and alsowith reference to a timing chart of FIG. 5. A routine illustrated inFIG. 4 is the automatic stop processing (Step ST102) of the engine 1described above with reference to FIG. 3, and is started at apredetermined timing (for example, when a flag showing the execution ofthe automatic stop processing is turned on). First, in Step ST201,injection of fuel by the injector 19 of each cylinder 2 is stopped (fuelcut).

Accordingly, when a fuel cut is started at time t0 of FIG. 5 and aninjection signal from the ECU 100 is no longer output, the combustiontorque of an air-fuel mixture is not generated in each cylinder 2 of theengine 1. As a result, the rotation speed of the crankshaft 13 thatrotates with inertia (and the crank rotation speed Nc illustrated by aone-dot chain line) decreases gradually. On the other hand, during thisperiod, the spark discharge caused by the ignition plug is continued,and an energization signal and a cutoff signal (hereinafter, the risingof a pulse illustrated in FIG. 5 is the energization signal and thefalling of the pulse is a cutoff signal, and these signals are alsoreferred to as an ignition signal together) are output from the ECU 100to the ignitor 22, respectively.

That is, in Step ST202 of the flow of FIG. 4, the crank rotation speedNc is calculated as a moving average, at a predetermined time, of therotation speed of the crankshaft 13 calculated from the crank signal. Inthe present embodiment, the crank rotation speed Nc is an average valueat the time when the crank rotation speed is shorter than the enginespeed. However, the crank rotation speed Nc may be an average value atthe time when the engine speed is calculated without being limited tothis average value.

Whether or not the crank rotation speed Nc calculated as described abovebecame equal to or less than the preset threshold value Nc1 isdetermined in Step ST203. When the crank rotation speed Nc becomes lowerthan the threshold value Nc1 as described above, the threshold value Nc1is not able to exceed the top dead center against an increase in thein-cylinder pressure of the cylinder 2. As a result, a rotation speed atwhich the crankshaft 13 is reversely operated is set in advance byexperiment or simulation.

The threshold value Nc1 varies by being influenced by individualvariations of the inertia or friction of rotating parts including thecrankshaft 13, changes in load caused by the operation of the alternatorand the engine auxiliary machine, the properties of engine oil, theamount of intake air filled into the cylinder 2, and the like.Therefore, threshold value Nc1 is set to a slightly higher value so thatthe occurrence of the reverse operation can be determined with a margin.

When the determination is negative (NO) in Step ST203, the processproceeds to Step ST204 in which the spark discharge caused by theignition plug is executed. That is, the energization signal is output ata predetermined crank angle before the top dead center sequentially fromthe cylinder 2 (the cylinder 2 in the compression stroke) that faces thetop dead center next, and the energization to the ignition coil 21 isstarted. Also, the cutoff signal to the predetermined crank angle afterthe top dead center (energization cutoff timing) is output, theenergization to the ignition coil 21 is cut off, ignition is performedby the ignition plug 20, and the routine is ended (END).

By doing as above, as described above with reference to FIG. 3, beforethe stop of rotation of the crankshaft 13 is determined in the stop andstart control routine (NO in Step ST103) or before the satisfaction ofthe engine restarting condition is determined (NO in Step ST108), theprocess returns to Step ST102 in which the automatic stop processing ofthe engine 1 is continued. That is, the processing of Steps ST201 toST203 of the flow of FIG. 4 is repeated.

As described above, the spark discharge caused by the ignition plug iscontinued for a while even after a fuel cut (times t0 to t1 of FIG. 5).In an example of FIG. 5, ignition is performed by ignition plugs 20 of asecond cylinder 2, the first cylinder 2, the third cylinder 2, and thefourth cylinder 2, and again the second cylinder 2 and the firstcylinder 2, and the unburned fuel is combusted. When the crank rotationspeed Nc decreases gradually and becomes equal to or less than thethreshold value Nc1 as illustrated at time t1 of FIG. 5, thedetermination is positive (YES) in Step ST203 of the flow of FIG. 4, theprocess proceeds to Step ST205, the spark discharge caused by theignition plug is stopped, and the routine is ended (END).

Accordingly, after time t1, as illustrated by a virtual line in FIG. 5,the ignition signal is no longer output and the energization to theignition coil 21 is no longer performed. Accordingly, in the example ofFIG. 5, after the top dead center (#3TDC) of the third cylinder 2 isexceeded at time t2, the crankshaft 13 is reversely operated due to arise of the in-cylinder pressure of the fourth cylinder 2 at time t3,and then is stopped (time t6) through a swing-back period (time t3 toT5).

When the crankshaft 13 is reversely operated as described above, thecrankshaft 13 does not reach the energization cutoff timing beyond thetop dead center (#4TDC) of the fourth cylinder 2. Thus, if the sparkdischarge caused by the ignition plug is continuing, the energizationtime to the ignition coil 21 becomes extremely long as illustrated by avirtual line. However, in the present embodiment, the spark dischargecaused by the ignition plug is already stopped and the energization tothe ignition coil 21 is not started. Thus, there is no concern that theenergization time becomes extremely long as described above.

By executing Steps ST203 to ST205 of the flow of the FIG. 4, the ECU 100constitutes an electronic control unit that cuts off the energizationafter elapse of a predetermined period from the start of energization tothe ignition coil 21 for each cylinder 2 of the engine 1, and causesspark discharge to be performed by the ignition plug 20. The electroniccontrol unit is configured such that the spark discharge caused by theignition plug is stopped from the cylinder 2 after the crank rotationspeed Nc decreases gradually after a fuel cut and reaches the presetthreshold value Nc1 or less.

In the present embodiment as described above, when the engine 1 of thevehicle is automatically stopped by the stop and start control, first, afuel cut is performed, and thereby, the rotation speed of the crankshaft13 decreases gradually. In this case, when the crank rotation speed Ncis higher than the threshold value Nc1, the spark discharge caused bythe ignition plug is continued, and thereby, the unburned fuel withinthe cylinder 2 is combusted. As a result, aggravation of emissions isfurther suppressed.

On the other hand, when the crank rotation speed Nc decreases graduallyand becomes the threshold value Nc1 or less, the spark discharge causedby the ignition plug is stopped, and thereby the wasteful powerconsumption is further suppressed. In the present embodiment, when thecrank rotation speed Nc becomes lower than the threshold value Nc1, thethreshold value Nc1 is set to such a rotation speed that the rotation ofthe crankshaft 13 is stopped and the crankshaft is reversely operated.Thus, by stopping the spark discharge caused by the ignition plug at thethreshold value Nc1 or less, the crankshaft 13 is no longer reverselyoperated during the energization to the ignition coil 21. As a result,the energization time can be further restrained from becoming extremelylong.

That is, by virtue of a suitable spark discharge caused by the ignitionplug after a fuel cut, the wasteful power consumption caused by unneededenergization to the ignition coil 21 can be further suppressed withoutcausing the aggravation of emissions at an automatic stop of the engine1. In addition, premature degradation of the ignition coil 21 resultingfrom the reverse operation of the crankshaft 13 immediately before theengine stop can be further restrained.

Modification Example 1

Modification Example 1 in which a timing for starting the energization(energization start timing) to the ignition coil 21 is retarded inaccordance with a decrease in the crank rotation speed Nc at anautomatic stop of the engine 1 will be described with reference to FIGS.6 and 7. Also in Modification Example 1, the configuration of thecontrol system of the engine 1, the procedure of the stop and startcontrol, and the like are the same as those of the above-describedembodiment, and different portions will be described below.

A routine of the automatic stop processing related to ModificationExample 1 is illustrated in FIG. 6, and first, the same processing asSteps ST201 to ST203 of the flow of FIG. 4 is performed in Steps ST301to ST303 after a start. When a negative determination (NO) that thecrank rotation speed Nc is higher than the threshold value Nc1 is madein Step ST303, the process proceeds to Step ST304, the spark dischargecaused by the ignition plug that is the same as Step ST204 is executed,and the routine is ended (END).

Accordingly, when a fuel cut is started at time t0 of FIG. 7 and therotation speed of the crankshaft 13 that rotates with inertia (and thecrank rotation speed Nc illustrated by a one-dot chain line) decreasesgradually, the spark discharge caused by the ignition plug is continuedand the ignition signal is output from the ECU 100 to the ignitor 22.Therefore, the unburned fuel is combusted within the cylinder 2 of theengine 1, and the aggravation of emissions is further suppressed.

When the crank rotation speed Nc decreases gradually and becomes equalto or less than the threshold value Nc1 as illustrated at time t1 ofFIG. 7, the determination is positive (YES) in Step ST303 of the flow ofFIG. 6, and the process proceeds to Step ST305. Here, while the sparkdischarge caused by the ignition plug is continued, the energizationstart timing (the output timing of the energization signal that is therising of the ignition signal) to the ignition coil 21 is retarded untilafter the top dead center of the cylinder 2, and the routine is ended(END).

Accordingly, in an example of FIG. 7, in the third cylinder 2 that facesa top dead center for the first time after time t1, the start ofenergization to the ignition coil 21 is delayed until after the top deadcenter (#3TDC) of the third cylinder 2. As a result, as illustrated by asolid line in FIG. 7, the energization to and the cutoff from theignition coil 21 are performed immediately after the top dead center(#3TDC) of the third cylinder 2 is exceeded at time t2, and the unburnedfuel is ignited by the ignition plug 20.

When the crankshaft 13 is reversely operated at time t3 due to a rise inthe in-cylinder pressure of the fourth cylinder 2, the energizationstart timing is not reached beyond the top dead center of the fourthcylinder 2. Thus, no ignition signal is output from the ECU 100 and theenergization to the ignition coil 21 is not performed. Therefore, asillustrated by a virtual line in FIG. 7, the energization time does notbecome extremely long and the premature degradation of the ignition coil21 from the above can be further restrained.

Hence, also in Modification Example 1, similar to the above-describedembodiment, by virtue of a suitable spark discharge caused by theignition plug after a fuel cut, the wasteful power consumption caused byunneeded energization to the ignition coil 21 can be further suppressedwithout causing the aggravation of emissions at an automatic stop of theengine 1, and the premature degradation of the ignition coil 21resulting from the reverse operation of the crankshaft 13 can be furtherrestrained.

The energization start timing may be gradually retarded in accordancewith a decrease in the crank rotation speed Nc from before the rotationspeed Nc becomes the threshold value Nc1 or less without retarding theenergization start timing to the ignition coil 21 after the crankrotation speed Nc becomes the threshold value Nc1 or less unlike theabove description. By doing as above, the energization time is shortenedas much as the retardation of the energization start timing. Thus,further suppression of the power consumption becomes possible.

Modification Example 2

Modification Example 2 in which the energization to the ignition coil 21is cut off in accordance with the reverse operation of the crankshaft 13without changing the spark discharge caused by the ignition plugaccording to a decrease in the crank rotation speed Nc like the aboveembodiment and Modification Example 1 will be described with referenceto FIGS. 8 and 9. Also in Modification Example 2, the configuration ofthe control system of the engine 1, the procedure of the stop and startcontrol, and the like are the same as those of the above embodiment, anddifferent portions will be described below.

The routine of the automatic stop processing related to the modificationexample 2 is illustrated in FIG. 8. First, in Step ST401 after start, afuel cut is performed similar to Step ST201 of the flow of FIG. 4, andin Step ST402, processing of the spark discharge caused by the ignitionplug is performed similar to Step ST204. Accordingly, when the rotationspeed of the crankshaft 13 decreases gradually after a fuel cut isstarted at time t0 of FIG. 9, the spark discharge caused by the ignitionplug is continued and the unburned fuel is combusted within the cylinder2.

In Step ST403 of the flow of FIG. 8, whether or not the ignition coil 21is being energized is determined. When a negative determination (NO)that the ignition coil is not being energized is made, the routine isended (END). On the other hand, when a positive determination (YES) thatthe ignition coil is being energized is made, the process proceeds toStep ST404 in which whether or not the crankshaft 13 is reverselyoperated this time is determined (crank reverse operation?). When thedetermination is negative (NO), the routine is ended (END).

Before the crankshaft 13 is reversely operated at time t3 in FIG. 9, theroutine is ended as described above, and the processing of Steps ST401to ST404 is repeated in a predetermined cycle. Even when the crankrotation speed Nc decreases to the threshold value Nc1 or less as in theabove embodiment and Modification Example 1 (time t1), the sparkdischarge caused by the ignition plug is continued. The energization tothe ignition coil 21 is performed also before and after the last topdead center (in the illustrated example, the top dead center #3TDC ofthe third cylinder 2) before the rotation of the crankshaft 13 isstopped.

After the top dead center (#3TDC) of the third cylinder 2 is exceeded asdescribed above, at time t3 of FIG. 9, the crankshaft 13 is reverselyoperated due to a rise in the in-cylinder pressure of the fourthcylinder 2, and does not reach the energization cutoff timing beyond thetop dead center (#4TDC). In an example of FIG. 9, since the energizationto the ignition coil 21 is started before the reverse operation of thecrankshaft 13, there is a possibility that the energization time maybecome extremely long as illustrated by a virtual line.

However, in this case, the determination is positive (YES) in StepsST403 and ST404 of FIG. 8, the process proceeds to Step ST405, theenergization to the ignition coil 21 is cut off, and the routine isended (END). That is, the cutoff signal is output from ECU 100 to theignitor 22, the pulse of the ignition signal falls at time t3 of FIG. 9,and the energization to the ignition coil 21 is cut off.

Hence, in Modification Example 2, similar to the above-describedembodiment and Modification Example 1, the aggravation of emissions atan automatic stop of the engine 1 can be restrained by continuing thespark discharge caused by the ignition plug even after a fuel cut. Also,when the crankshaft is reversely operated after the energization to theignition coil 21 is started for that purpose, the energization isimmediately cut off. Thus, from the above description, the energizationtime does not become extremely long, the wasteful power consumption canbe further suppressed, and the premature degradation of an ignition coilcan be further restrained.

OTHER EMBODIMENTS

The description of the embodiment described above is merely an exampleand is not intended to limit the configuration, application, and thelike of the present disclosure. For example, in the above embodiment,when the crank rotation speed Nc becomes the threshold value Nc1 or lesswhen the engine 1 is automatically stopped by the stop and startcontrol, the spark discharge caused by the ignition plug is stopped.However, the present disclosure is not limited to this, and the sparkdischarge caused by the ignition plug may be stopped, for example, whenthe engine speed becomes equal to or less than below the thresholdvalue.

In the above embodiment and Modification Example 1, when the crankrotation speed Nc becomes the threshold value Nc1 or less, the sparkdischarge caused by the ignition plug is stopped, or the energizationstart timing to the ignition coil 21 is retarded. However, the aspect ofthe present disclosure is not limited to this, and for example, theguard time of the energization time set for the protection of theignition coil 21 may be shortened.

In Modification Example 1 of the above embodiment, the energizationstart timing to the ignition coil 21 is retarded in accordance with adecrease in the crank rotation speed Nc. In Modification Example 2, theenergization to the ignition coil 21 is cut off in accordance with thereverse operation of the crankshaft 13. However, the configurations ofModification Examples 1 and 2 may be appropriately combined together.

For example, the energization start timing to the ignition coil 21 maybe retarded in accordance with a decrease in the crank rotation speed Ncafter a fuel cut, and when the crank rotation speed Nc becomes thethreshold value Nc1 or less, the spark discharge caused by the ignitionplug may be stopped. For example, the energization start timing to theignition coil 21 may be retarded in accordance with a decrease in thecrank rotation speed Nc after a fuel cut, and the energization to theignition coil 21 may be cut off in accordance with the reverse operationof the crankshaft 13.

In the above embodiment, the automatic stop condition is set to includea case where the vehicle speed is equal to or lower than thepredetermined threshold value (in a case where the engine is consideredto be immediately before a stop and a case where the engine isconsidered to be substantially stopped). However, the aspect of thepresent disclosure is not limited to this and can also be applied to acase where the engine 1 is automatically stopped and restarted duringthe traveling of a vehicle. The aspect of the present disclosure can beapplied to the case of a manual stop as well as the automatic stop ofthe engine 1.

In the above embodiment, a case where the aspect of the presentdisclosure is applied to the in-cylinder injection type gasoline engine1 mounted on a vehicle has been described. However, the aspect thepresent disclosure is not limited to this and can also be applied to aport injection type gasoline engine. The aspect of the presentdisclosure can also be applied to a diesel engine, an alcohol engine, agas engine, or the like without being limited to the gasoline engine.

In the aspect of the present disclosure, the wasteful power consumptioncan be further suppressed without causing the aggravation of emissionsat an engine stop, and the premature degradation of the ignition coilcan be further restrained. Thus, for example, the aspect of the presentdisclosure is highly effective when being applied to stop and startcontrol or the like of an engine mounted on an automobile.

What is claimed is:
 1. An engine control device comprising an electroniccontrol unit configured to perform a spark discharge with an ignitionplug for each cylinder by cutting off energization after elapse of apredetermined period from start of energization to an ignition coil foreach cylinder of the engine, stop the spark discharge caused by theignition plug for each cylinder after supply of fuel to the engine isstopped when operation of the engine is stopped, and control theignition plug so as to stop the spark discharge caused by the ignitionplug from a cylinder after a rotation speed of a crankshaft decreasesgradually and the rotation speed of the crankshaft reaches a presetthreshold value or less, after the stop of the supply of fuel to theengine.
 2. The engine control device according to claim 1, wherein thethreshold value is set to such a rotation speed that the crankshaft isreversely operated in accordance with a compression reaction force ofthe cylinder when the rotation speed of the crankshaft becomes lowerthan the threshold value.
 3. An engine control device comprising anelectronic control unit configured to perform a spark discharge with anignition plug for each cylinder by cutting off energization after elapseof a predetermined period from start of energization to the ignitioncoil for each cylinder of the engine, stop the spark discharge caused bythe ignition plug for each cylinder of the engine after supply of fuelto the engine is stopped when operation of the engine is stopped, andretard an energization start timing to the ignition coil as a rotationspeed of a crankshaft becomes lower when the rotation speed of thecrankshaft decreases gradually after the stop of the supply of fuel tothe engine.
 4. The engine control device according to claim 3, whereinthe electronic control unit is configured to retard the energizationstart timing to the ignition coil until after a compression top deadcenter of a cylinder when the rotation speed of the crankshaft becomesequal to or lower than a preset threshold value.
 5. An engine controldevice comprising an electronic control unit configured to perform aspark discharge with an ignition plug for each cylinder by cutting offenergization after elapse of a predetermined period from start ofenergization to an ignition coil for each cylinder of the engine, stopthe spark discharge caused by the ignition plug for each cylinder of theengine after supply of fuel to the engine is stopped when operation ofthe engine is stopped, and cut off the energization to the ignition coileven before the elapse of the predetermined period in a case where acrankshaft is reversely operated after the start of energization to theignition coil.